Wireless communications device allowing a soft handoff procedure in a mobile communications system

ABSTRACT

A wireless communications device includes an antenna that receives a first signal at a first frequency and a second signal at a second frequency and converts the first and second signals into a composite signal. A first oscillator outputs a first oscillator signal at a first frequency and a second oscillator outputs a second oscillator signal at a second frequency. A demodulator receives the composite signal and the first and second oscillator signals. The oscillator signals are selected so that the demodulator generates a low frequency signal with components of the first and second signals occupying a common frequency band. The wireless communications device allows executing a “Soft Handoff” even when the first and second frequencies are different.

[0001] This application is a continuation of U.S. application Ser. No.09/342,165, filed on Jun. 28, 1999, the entirety of which is herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention generally relates to a communications system. Moreparticularly, the invention relates to a wireless communications deviceand a method of receiving radio frequency signals within acommunications system.

[0004] 2. Description of the Related Art

[0005] One example of a communications system is a wirelesscommunications system which can be a cellular mobile communicationssystem. The cellular mobile communications system is implemented in ageographical area and logically divided into individual service cells. Afixed transceiver station such as a base station defines at least onecell and is connected to a base station controller. Mobile stations,such as hand-held or car-based cellular phones, move freely within thegeographical area covered by a cell. The mobile stations not only movewithin a single cell, but also from one cell to a neighboring cell.

[0006] The base station handles all telephone traffic to and from thosecellular phones which are currently located in the cell. The basestation that serves a cellular phone is typically the one which isclosest to the cellular phones and, thus, provides in many cases thebest radio communications path to the cellular phones.

[0007] The cellular phones and the serving base station exchange radiosignals in accordance with a communications protocol defined for a givencommunications system. The radio signals have frequencies withinfrequency bands that are assigned to the cells. In one example of acommunications protocol, the radio signals can be structured in framesand channels.

[0008] In conventional Code Division Multiple Access (CDMA) systems, apilot channel is defined for communications between the base stationsand the cellular phones. The pilot channel carries no information, butprovides the cellular phone, for example, with a reference for time,phase, and signal strength. The cellular phone constantly evaluates thestrengths of the pilot channels of the serving and neighboring basestations to determine potential base stations. When the strength of thepilot channel of the serving base station falls below a predeterminedthreshold and the strength of the pilot channel of the neighboring basestation exceeds a predetermined threshold, a handoff procedure isinitiated. The procedure that transfers the mobile station from one cellto another cell, without dropping a call or losing information, is oftencalled “Soft Handoff.”

[0009] In many conventional Soft Handoff procedures, the base stationsof neighboring cells use the same frequencies. This requirement,however, limits the number of mobile stations that can be served by onebase station. For example, if two neighboring base stations operate atdifferent frequencies, a so-called “Hard Handoff” procedure typicallytakes place which causes a break in an existing connection and mayresult in a loss of information.

SUMMARY OF THE INVENTION

[0010] An aspect of the invention involves a wireless communicationsdevice for a communications system. The wireless communications includesan antenna, which receives a first signal at a first radio frequency anda second signal at a second radio frequency, and convert the first andsecond signals into a composite radio frequency (RF) signal. A firstoscillator is operable to output a first oscillator signal at a firstfrequency, and a second oscillator is operable to output a secondoscillator signal at a second frequency. A demodulator is coupled toreceive the composite RF signal and the first and second oscillatorsignals. The oscillator signals are selected so that the demodulatorgenerates a low frequency signal with components of the first and secondsignals occupying a common frequency band.

[0011] Another aspect of the invention involves a wirelesscommunications device having a first input configured to receive aninput signal which comprises a first component allocated within a firstfrequency band and a second component allocated within a secondfrequency band. A first oscillator is configured to generate a firstoscillator signal at a first oscillator frequency, and a secondoscillator is configured to generate a second oscillator signal at asecond oscillator frequency. A mixer is configured to receive the inputsignal, the first oscillator signal, and the second oscillator signal,and to convert at least a portion of the first component and at least aportion of the second component to a third frequency band.

[0012] A further aspect of the invention involves a device having atleast a first terminal which is configured to receive a first signalwithin a first frequency band from a first source and a second signalwithin a second frequency band from a second source. At least a secondterminal is configured to receive at least a first reference signal anda second reference signal. A modulator in communication with the firstand second terminals is configured to generate a first differencecomponent within a third frequency band. The first difference componentcomprises the difference between a portion of the first signal withinthe first frequency band and the first reference signal. The modulatoris further configured to generate a second difference component withinthe third frequency band, the second difference component comprising thedifference between a portion of the second signal within the secondfrequency band and the second reference signal.

[0013] Another aspect of the invention involves a wirelesscommunications device having a first input to receive an input signalwhich comprises a first component having a first frequency allocatedwithin a first frequency band and a second component having a secondfrequency allocated within a second frequency band. A first oscillatoris configured to generate a first oscillator signal at a firstoscillator frequency, and a second oscillator is configured to generatea second oscillator signal at a second oscillator frequency. A mixer isconfigured to receive the input signal, the first oscillator signal, andthe second oscillator signal, and to convert at least a portion of thefirst component and at least a portion of the second component into athird frequency band. The portion of the first component has a firstdifference frequency corresponding to a difference between the firstfrequency and the first oscillator frequency, and the portion of thesecond component has a second difference frequency corresponding to adifference between the second frequency and the second oscillatorfrequency. The first difference frequency is approximately equal to thesecond difference frequency, both located within the third frequencyband.

[0014] A further aspect of the invention involves a method of receivingradio frequency (RF) signals with a wireless communications device thatis operable in a communications system. The device receives a firstsignal within a first frequency band from a first source, and a secondsignal within a second frequency band from a second source. Further, thedevice transforms the first and second signal into a third frequencyband, and processes the frequency-transformed first and second signalsin order to maintain communications with the first and second sources.

[0015] Another aspect of the invention involves a method of receivingradio frequency (RF) signals. A first RF signal has a first radiofrequency and originates from a first transmitter station, and a secondRF signal has a second radio frequency and originates from a secondtransmitter station. The first and second RF signals are received andconverted into a composite signal. A first oscillator signal isgenerated having a first oscillator frequency, which is selected to havea first frequency difference to the first radio frequency. A secondoscillator signal is generated having a second oscillator frequency,which is selected to have a second frequency difference to the firstradio frequency. The composite signal is mixed with the first and secondoscillator signals to generate an intermediate frequency signal. Theintermediate frequency signal comprises a component of the first RFsignal and a component of the second RF signal with the components beinglocated within a common frequency band. The intermediate frequencysignal is processed to generate a first baseband signal and a secondbaseband signal. The first baseband signal corresponds to the first RFsignal and the second baseband signal corresponds to the second RFsignal.

[0016] For purposes of summarizing the invention, certain aspects,advantages and novel features of the invention have been describedherein. Of course, it is to be understood that not necessarily all suchadvantages may be achieved in accordance with any particular embodimentof the invention. Thus, the invention may be embodied or carried out ina manner that achieves or optimizes one advantage or group of advantagesas taught herein without necessarily achieving other advantages as maybe taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and other aspects, advantages, and novel features of theinvention will become apparent upon reading the following detaileddescription and upon reference to the accompanying drawings.

[0018]FIG. 1 shows an exemplary infrastructure of a mobilecommunications system.

[0019]FIG. 2 shows infrastructures of two separated mobilecommunications systems.

[0020]FIG. 3 is an illustration of a cellular phone.

[0021]FIG. 4 is an illustration of a receive path of a cellular phone.

[0022]FIG. 5 is an illustration of a receiver included in the receivepath shown in FIG. 4.

[0023]FIG. 6 is a spectrum of an intermediate frequency signal.

[0024]FIG. 7 is a flow chart illustrating a handoff procedure.

[0025]FIG. 8 is an illustration of an embodiment of a receiver mixermodule.

[0026]FIGS. 9 and 10 are illustrations of embodiments of mixers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027]FIG. 1 shows an illustration of a mobile communications system 1manufactured by a public or private telephone company (“serviceprovider”). The telephone company can provide access to a publicswitched telephone network (PSTN). The operating telephone companydetermines parameters of the mobile communications system 1 including,but not limited to, geographical coverage area, communicationsstandards, frequency, system capacity, and the like.

[0028] In one embodiment, the mobile communications systems 1 is acellular mobile communications system configured to operate as a CodeDivision Multiple Access (CDMA) system. Such an exemplary mobilecommunications system 1 is referred to as a cellular system. Anembodiment of the present invention is hereinafter described withreference to, but not limited to, such a cellular system 1. It iscontemplated that the present invention is applicable in other mobilecommunications systems, such as systems known as a personalcommunications service using CDMA technology (PCS/CDMA).

[0029] The cellular system 1 of FIG. 1 includes a plurality of basestations B1, B2, each defining a cell. For instance, the base station B1defines a cell C1 and the base station B2 defines a cell C2. Neighboringcells C3, C4 are shown for illustrative purposes. As indicated, thecells C1-C4 overlap to a certain degree in the illustrated embodiment.It is contemplated that in other embodiments, the cells C1-C4 can moreor less overlap depending on the geographical area.

[0030] Communication lines L1, L2 connect the base stations B1, B2 to abase station controller BC1, which controls the base stations B1, B2 andconnects the cellular system 1 to a switching center in the domain ofthe service provider or to a (wire-based) public telephone system(PSTN). In FIG. 1, this connection is illustrated as “TO SWITCH.” Thecommunications lines L1, L2 are, for example, fiber-optic cables,twisted pair lines, coaxial cables, or combinations thereof typicallyused for communications lines. In certain embodiments, thecommunications lines L1, L2 can represent wireless bi-directional radioconnections and the like.

[0031] The cellular system 1 further includes at least one mobilestation 3 which can freely move within the cellular system 1. It iscontemplated that a plurality of mobile stations 3 can be active orinactive within the cellular system 1. The mobile station 3 can be, forexample, a wireless phone, a handheld cellular phone, a cellular phonemounted in a vehicle, or any other wireless device (e.g., a pager) whichcan be used in a cellular system 1. The mobile station 3 can move freelywithin each cell C1-C4 and between the cells C1-C4. In FIG. 1, themobile station 3 is indicated as a handheld cellular phone, which islocated within the cell C1 and served by the base station B1. The mobilestation 3 is hereinafter referred to as the phone 3.

[0032] As shown, the phone 3 is currently located within the cell C1 andhas a bi-directional radio connection with the base station B1. Thebi-directional radio connection indicates that calls to and from thephone 3 are handled by the base station B1. The base station B1 istherefore referred to as the serving base station B1. In one embodiment,the radio connection is established through a signal S1 having afrequency band around a carrier frequency f1. In one embodiment, thecarrier frequency f1 is approximately 880 MHz.

[0033] When the phone 3 moves within the cellular system 1, the phone 3is handed off from one cell to another. This is referred to as anintra-system handoff. Before the handoff, the phone 3 communicates withthe serving base station B1 at a “pre-handoff” frequency f1, and afterthe handoff, the phone 3 communicates with the new base station B1 at a“post-handoff” frequency f2 of a signal S2. Depending on theinfrastructure of the cellular system 1, the post-handoff frequency f2can be the same as the pre-handoff frequency f1, or the post-handofffrequency f2 can be different from the pre-handoff frequency f2.

[0034]FIG. 2 illustrates a scenario in which the geographical areacovered by the cellular system 1 is also covered by a second mobilecommunications system 100. The second mobile communications system 100is under the control of a different service provider whoseinfrastructure is in one embodiment generally similar to theinfrastructure of the cellular system 1. In FIG. 2, the infrastructureof the cellular system 1 is as shown in FIG. 1 and the phone 3 is incommunication with the serving base station B1.

[0035] An exemplary cell structure of the second mobile communicationssystem 100 is indicated through dashed lines. The second mobilecommunications system 100 has a plurality of base stations BS1, BS2,which are connected to a controller BC2. The base station BS1 serves acell C5 and the base station BS2 serves a cell C6. The second mobilecommunications system 100 has assigned frequencies (e.g., f3) for thecells that can be different from the frequencies assigned to thecellular system 1. For example, the second mobile communications system100 can be a PCS/CDMA system operating at a frequency band aroundapproximately 1800 MHz and the cellular system 1 can be a cellular CDMAsystem operating at a frequency band between approximately 800 MHz andapproximately 900 MHz.

[0036] In addition to the intra-system handoff described with referenceto FIG. 1, in some applications, the phone 3 can be configured to move(roam) freely between the cellular system 1 and the mobilecommunications system 100 (e.g., a PCS/CDMA system) as indicated in FIG.2. That is, the phone 3 has the capability of seamless roaming, forexample, from a cellular CDMA system to a PCS/CDMA system. This isreferred to as an “inter-system handoff.” Under these circumstances, thephone 3 is handed off from the cellular CDMA system to the PCS/CDMAsystem and the pre-handoff frequency f1 and the post-handoff frequencyf3 are different.

[0037] Referring to FIGS. 1 and 2, independent if an intra-systemhandoff or an inter-system handoff occurs, the capability of the desired“Soft Handoff” is maintained within the systems 1, 100. As describedbelow in greater detail, the phone 3 includes two local oscillatorswhich can be tuned to appropriate frequencies so that a radio connectionwith the base station of a “target” cell can be made before the radioconnection with the (previous) serving base station is broken. The firstlocal oscillator is tuned to a frequency f_(LO1), and the second localoscillator can be tuned to a frequency f_(LO2).

[0038] The frequencies f_(LO1), f_(LO2) are selected so that thefrequencies f1, f2 of the signals S1, S2 are down converted tofrequencies within a common frequency band. If the frequencies f1, f2are approximately the same, the frequencies f_(LO1), f_(LO2) are alsoapproximately the same. Correspondingly, if the frequencies f1, f2 aredifferent, the frequencies f_(LO1), f_(LO2) are different. The lattercase occurs, for example, when the signal S1 originates from a cellularCDMA system (f1=880 MHz) and the signal S2 originates from a PCS system(f2=1960 MHz). In this example, the frequency f_(LO1) can beapproximately 680 MHz and the frequency f_(LO2) can be approximately1760 MHz so that after the down conversion resulting differencesfrequencies (880 MHz-680 MHz, and 1960 MHz-1760 MHz) are within the samefrequency band of about 200 MHz.

[0039] While the phone 3 is active or in a stand-by mode, the phone 3constantly evaluates the signal strengths received in the pilot channelsof the serving base station B1 and the neighboring base stations, suchas the base station B2, to determine potential base stations for anupcoming handoff. When the signal strength of the pilot channel of theserving base station B1 falls below a predetermined threshold and thesignal strength of the pilot channel of another base station B2 exceedsa predetermined threshold, the handoff procedure is started. In case thephone 3 is in the stand-by mode, the evaluation of the signal strengthsof the pilot channels serves to determine which base station B1, B2, BS1will be the serving base station if the phone 3 becomes active.

[0040] Focusing on an embodiment of a cellular CDMA system which has aninfrastructure as shown in FIG. 1, the base station B1 transmits andreceives radio signals within a frequency band around the carrierfrequency f1 assigned to the cell C1. For instance, the base station B1transmits at a frequency of approximately 880 MHz and receives at afrequency of approximately 835 MHz. Similarly, the base station B2transmits at 1960 MHz and receives radio signals within a frequency bandaround a carrier frequency f2 of approximately 1880 MHz assigned to thecell C2. It is contemplated that in another embodiment, the basestations B1, B2 can operate within the same frequency band, which isassigned to neighboring cells.

[0041]FIG. 3 schematically illustrates one embodiment of the phone 3.The phone 3 includes an antenna 11, a display, and a keypad. A portionof the case of the phone 3 is cut away to show a motherboard 5 of thephone 3 with an integrated circuit 10 which includes an RF receiver, ora portion thereof, as described below. The integrated circuit 10 ishereinafter generally referred to as the RF receiver 10. Although notshown in FIG. 1, those skilled in the art will appreciate that the phone3 comprises a central processor unit (CPU) and plurality of othercomponents and functional modules of conventional phones.

[0042]FIG. 4 shows a schematic illustration of a receive path and atransmit path. Both paths are associated with the antenna 11 to receiveand transmit signals. In the illustrated embodiment, the transmit pathincludes a conventional transmitter for RF signals, and the receive pathcomprises the RF receiver 10 (hereinafter referred to as the receiver10), a signal processing module 7 and a speaker 9. The receiver 10 isinterconnected between the antenna 11 and the signal processing module 7which is connected to the speaker 9.,

[0043] The receiver 10 includes several groups of amplifiers which areseparated by frequency-changing circuits (e.g., mixers, modulators ordemodulators) to extract information carried by a weak signal voltagethat appears at terminals of the antenna 11. The antenna 11 receives thesignals S1, S2, for example, from the serving base station B1 of thecell C1 and the target base station B2 of the cell C2, and converts thesignals S1, S2 to a composite electrical signal. The compositeelectrical signal includes the frequencies f1, f2 which can have same ordifferent values depending on the infrastructure of the systems 1, 100.As the frequencies f1, f2 are in the radio frequency range (e.g., 880MHz, or 1960 MHz), the composite electrical signal is hereinafterreferred to as the “composite RF signal.”

[0044] As described below in greater detail, the receiver 10 convertsthe composite RF signal, which includes the signals S1, S2, from aninitial high frequency (RF) range down to a lower frequency range, thebaseband. In one embodiment, the down conversion process includes twostages. A first stage down converts the composite RF signal from the RFrange to an intermediate frequency range, and a second stage downconverts the composite RF signal from the intermediate frequency rangeto the baseband. The down conversion process is also known as“heterodyning.” Therefore, the receiver 10 outputs the signals S1, S2 asbaseband signals, which are input to the signal processing module 7 forfurther processing.

[0045]FIG. 5 shows a schematic illustration of the receiver 10. In oneembodiment, the receiver 10 is implemented as an integrated circuit andconfigured to operate at a voltage between 2.7 volts and 5 volts. Thevoltage can be provided by a re-chargeable battery, or if the phone 3 ismounted to a car, from the car battery. However, those skilled in theart will appreciate that the receiver 10 can be configured to operatedat lower or higher voltages. Further, it is contemplated that not allcomponents of the receiver 10 are necessarily integrated in theintegrated circuit. That is, a specific implementation of the receiver10 may have discrete and isolated components in combination withintegrated circuits.

[0046] The embodiment of the receiver 10 shown in FIG. 5 shows thereceiver 10 in a single-ended embodiment. In another embodiment, thereceiver 10 can be implemented in a differential embodiment. In someapplications, the differential embodiment is preferred to differentiatethe actual signal from noise and, thus, to improve the signal-to-noiseratio. If the receiver 10 is implemented in the differential embodiment,the components of the receiver 10 are connected between two differentiallines which are typically referred to as “positive” and “negative”, or“+” and “−.” Compared to the single-ended embodiment, the components areduplicated for each differential line in the differential embodiment.The principal operation, however, corresponds to the operation of thesingle-ended embodiment.

[0047] Focusing on the single-ended implementation of the receiver 10,the receiver 10 includes a mixer module 12, which down converts thecomposite RF signal to the baseband, and a baseband processor 38. Themixer module 12 has an input 13 and outputs 15 a, 15 b to connect themixer module 12 to the antenna 11 and the baseband processor 38,respectively. The baseband processor 38 has an output 19, which isconnectable to the signal processing module 7.

[0048] In one embodiment, the mixer module 12 comprises a combination ofan amplifier 14 and a mixer 18 for signal amplification and frequencydown conversion. The amplifier 14 is, for example, a low-noise amplifier(LNA) that receives the composite RF signal, amplifies the composite RFsignal, and feeds the amplified RF signal to the mixer 18. In addition,the mixer 18 receives oscillator signals LO1, LO2 generated by twoseparate local oscillators 34, 36. The oscillator signals LO1, LO2 are,for example, sinusoidal signals each having a constant amplitude andfrequency.

[0049] The mixer 18 multiplies the composite RF signal and theoscillator signals LO1, LO2, and the various signal components mix witheach other. The oscillator signal LO1 mixes with the signals S1, S2 ofthe composite RF signal and the oscillator signal LO2 mixes with thesignals S1, S2. As is known in the art, this mixing process results in asignal that includes a variety of different frequencies. These differentfrequencies include the original frequencies f1, f2, f_(LO1), f_(LO2),their harmonics, for example, 2f1, 2f2, 2f_(LO1), 2f_(LO2), and theirsums and differences, for example, f1±f_(LO1), f2±f_(LO2).

[0050] In one embodiment, the difference frequencies −f1+f_(LO1),−f2+f_(LO2) are of interest. The oscillator frequencies f_(LO1), f_(LO2)are selected so that the difference frequencies −f1+f_(LO1), −f2+f_(LO2)fall within the same frequency band and have approximately the samevalue, i.e., (−f1+f_(LO1))≈(−f2+f_(LO2)). This frequency value ishereinafter referred to as the “intermediate frequency,” which is lowerthan the initial frequencies f1, f2, and written as “f1˜f_(LO1),f2˜f_(LO2).” The local oscillators 34, 36 can be tuned to appropriateoscillator frequencies f_(LO1), f_(LO2) that fulfill the requirement of(f1˜f_(LO1))≈(f2˜f_(LO2)). It is contemplated that this requirementgenerally indicates that the differences (f1˜f_(LO1); f2˜f_(LO2)) fallwithin the same frequency band and that the differences (f1˜f_(LO1);f2˜f_(LO2)) can be in the MHz range.

[0051] Because the mixer 18 generates an output signal that comprises avariety of different frequencies, a filter 20 is connected to the mixer18 in order to block frequencies other than the intermediate frequencyf1˜f_(LO1), f2˜f_(LO2). The signal output from the filter 20 is referredto as the intermediate frequency (IF) signal.

[0052] In the illustrated embodiment, the mixer module 12 furtherincludes a filter 16, an amplifier 22, and two mixers 26, 28. The filter16 is connected between the mixer 18 and the amplifier 14 connected tothe input 13. The mixer 18 is connected to the filter 16 to receive thebandlimited composite RF signal and to the local oscillators 34, 36. Asshown, the filter 16 is a bandpass filter which limits the bandwidth ofthe composite RF signal received from the amplifier 14 to blockundesired frequency components and to reduce noise in the composite RFsignal. The undesired frequency components can be caused, for example,by nonlinearities of the amplifier 14 that result in intermodulationproducts. In one embodiment, the passband of the filter 16 is about 25MHz to allow passage of a receive band between about 850 MHz and 900MHz, more precisely between 869 MHz and 894 MHz, and to blockfrequencies outside of this receive band.

[0053] The local oscillators 34, 36 are in one embodiment conventionallocal oscillators configured to operate at the different oscillatorfrequencies f_(LO1), f_(LO2). The oscillator signals LO1, LO2 can besinusoidal signals each having a frequency between 500 MHz and 2.5 GHz.In one embodiment, the oscillator signal LO1 has a frequency f_(LO1) ofapproximately 955 MHz and the oscillator signal LO2 has a frequencyf_(LO2) of approximately 960 MHz. These values for the frequenciesf_(LO1), f_(LO2) correspond to radio frequencies of 875 MHz and 879 MHz,respectively.

[0054] The oscillator signals LO1, LO2 are tunable to adapt to otherphone systems which operate, for example, at carrier frequencies ofabout 1800 MHz or 1900 MHz. Alternatively, the phone 3 can be a dualband cellular phone which can operate within different frequency bands,for example, 800 MHz, 900 MHz, 1800 MHz, or 1900 MHz. Independent ofwhat carrier frequencies the signals S1, S2 have, the frequencies of thesignals LO1, LO2 are generally selected so that the difference(f1˜f_(LO1)) is approximately in the same frequency band as thedifference (f2˜f_(LO2)). An exemplary signal output from the filter 20,in which the down converted signals S1, S2 fall within the samefrequency band, is shown in FIG. 6 and described below.

[0055] Although FIG. 5 shows the local oscillators 34, 36 as belongingto the mixer module 12, it is contemplated that the local oscillators34, 36 may be located outside the mixer module 12 and at other locationswithin the phone 3. If the mixer module 12 is implemented as anintegrated circuit, the local oscillators 34, 36 are typically locatedoff-chip. In one embodiment, the local oscillators 34, 36 areconventional frequency synthesizers whose frequencies are referenced topiezoelectric crystals. The synthesizers are tunable within apredetermined range. It is contemplated that other types of localoscillators, such as voltage controlled oscillators (VCO), can be usedto generate the desired IF signal.

[0056] An output of the mixer 18 is connected to the filter 20, which isin the illustrated embodiment a bandpass filter. The filter 20 has apassband between approximately 1.25 MHz and approximately 85 MHz. Inanother embodiment, for example, in direct conversion receivers, thefilter 20 is implemented as a low-pass filter, which has, for example, acut-off frequency of approximately 0.63 MHz. The filter 20 selects thedesired frequency band around the intermediate frequency f1˜f_(LO1),f2˜f_(LO2), and blocks frequencies, which are located outside thepassband, or are higher than the cut-off frequency. It is contemplatedthat other values for the passband or the cut-off frequency can bechosen.

[0057] In one embodiment, the amplifier 22 is connected to a controlline 24 to receive an automatic gain control signal AGC from a centralcontroller (not shown) of the phone 3. The control signal AGC controlsthe amplifier 22 to amplify the IF signal with a desired gain. Theamplifier 22 is operable at a gain between +45 dB and −45 dB to amplifythe IF signal to a predetermined level over the entire dynamic range ofthe receiver

[0058] In the illustrated embodiment, the mixers 26, 28 form aconversion module located within the mixer module 12, and connected toan output of the amplifier 22. Those skilled in the art, however, willappreciate that in another embodiment the mixers 26, 28 can be locatedwithin the baseband processor 38. An output of the mixer 26 is connectedto the output 15 a and an output of the mixer 28 is connected to theoutput 15 b. A local oscillator 32 generates an oscillator signal LO3that is, for example, a sinusoidal signal having an oscillator frequencyf_(LO3). The oscillator signal LO3 is input to the mixer 26 and, with a90 degrees phase shift, to the mixer 28. That is, in one embodiment, themixers 26, 28 receive signals having a sin function and a cosinefunction.

[0059] The oscillator frequency f_(LO3) is selected so that the IFsignal, having a frequency with (f1˜f_(LO1))≈(f2˜f_(LO2)), is downconverted to the baseband at a frequency f_(B) of approximately 0-630kHz. Similar to the first down conversion stage implemented through themixer 18, the oscillator frequency f_(LO3) is selected so that the IFsignal is downconverted to baseband “In phase” (I) and “Quadrature” (Q)outputs. The second down conversion stage, implemented by the mixers 26,28, splits the IF signal into the two components I, Q which correspondto I/Q components containing information transmitted by the basestations B1, B2. The components I, Q are input to the baseband processor38 which performs the processing necessary to convert the received CDMAsignal back to an uncoded (“de-spread”) signal and extracts thevoice/data signals.

[0060] As is known to the person skilled in the art, CDMA is a spreadspectrum technique for multiple access. The CDMA technique is sometimesexplained with reference to a situation encountered at a cocktail party.Like in a cellular CDMA system, all guests are talking in the same roomsimultaneously, but every conversation occurs in a different language.If one guest does not understand these languages, they would all soundlike “noise” from the guest's perspective. However, if the guest wouldknow the “code,” i.e., the appropriate language, the guest could “filterout” the unknown languages (noise) and listen only to the conversationin the language the guest understands.

[0061] Besides the language (code) problem, the guest may encounteranother problem. Even with knowledge of the appropriate language, theguest may not hear the complete conversation because either the speakerdoes not speak loud enough, or the other speakers speak too loud. Theguest can signal to the speaker to speak louder, but can also signal tothe other guests to speak more softly. The cellular CDMA system appliesa corresponding “power control” process and filter function.

[0062] Referring to a cellular CDMA system, multiple telephoneconversations are spread across a wide segment of a (broadcast)frequency spectrum at a transmitter and “de-spread” at the receiver.Each user (telephone call) is assigned a unique code to modulatetransmitted data. The code is unique and distinguishes a specific callfrom the multitude of other calls simultaneously transmitted over thesame broadcast spectrum. The code is a long sequence of ones and zerossimilar to the output of a random number generator of a computer. Thecomputer generates the code using a specific algorithm and the numbersappear to be random. Because the codes are nearly random, there is verylittle correlation between the different codes. In addition, there isvery little correlation between a specific code and any time shift ofthat same code.

[0063] Thus, the distinct codes can be transmitted over the same timeand the same frequencies and the signals can be decoded at the receiverby correlating the received signal which is the sum of all transmittedsignals with each code. As the receiver has the correct code, it candecode the received signal, i.e., the receiver can select “its”conversation from all the others. With CDMA, all users on a 1.25MHz-wide channel can share the same frequency spectrum because eachuser's conversation is differentiated utilizing CDMA's unique digitalcodes. That same 1.25 MHz of frequency spectrum is re-used in each cellin the network.

[0064] In one embodiment, the base station B1, B2, BS1, BS2 communicateswith each phone every 1.25 milliseconds to control its power level.Every 1.25 milliseconds, the base station B1, B2, BS1, BS2 instructs thephone 3 to increase or decrease its power, depending upon its distancefrom the base station B1, B2, BS1, BS2. The CDMA phone 3 transmits onlythe minimum power required to maintain a communications link. If thephone 3 is too far away from the serving base station B1, and thephone's transmitted power can not be increased, or if a neighboring basestation B2, BS1, BS2 provides for a better radio connection, the phone 3is handed off to one of the neighboring cell/base stations B2, BS1, BS2.

[0065] The receiver 10 illustrated in FIG. 5 monitors the pilot channelsreceived at the frequencies f1, f2. The pilot channels are downconverted to the baseband as described above and the signal strength ofthe pilot channels is determined independently. The signal strengths ofthe pilot channels are compared to a threshold value. If the signalstrength of the target cell's pilot channel is above the thresholdvalue, the controller BC1 (FIG. 1) initiates the handoff procedure.

[0066]FIG. 6 is a graph illustrating an exemplary spectrum of the IFsignal, wherein the amplitude of the IF signal is shown as a function ofthe frequency f. For example, a spectrum analyzer is connected to anoutput of the filter 20 to measure the spectrum. As the IF signal passedthrough the filter 20, the spectrum of the IF signal is band limitedhaving a bandwidth B of approximately ±630 kHz.

[0067] As described above, the IF signal is a composite signalcomprising the signals S1, S2 that originate from two different basestations, for example, the serving base station B1 and the target basestation B2. In the illustrated embodiment, the amplitude of the signalS2 is higher than the amplitude of the signal S1. The signals S1, S2 canbe separated through correlation with the respective codes as describedabove. When the signals S1, S2 are separated, the signal strengths inthe pilot channels can be determined.

[0068]FIG. 7 is a flow chart illustrating the operation of the phone 3when it receives RF signals originating from, for example, two differentbase stations B1, B2, BS1, BS2. Referring to FIG. 1, for the followingdescription it is assumed the phone 3 moves from the serving cell C1 tothe target cell C2. The procedure is initialized at state 800.

[0069] Proceeding to state 802, the receiver 10 receives the signals S1,S2 from the serving base station B1 of the cell C1, and the target basestation B2 of the cell C2. The signal S1 has the frequency f1 and thesignal S2 has the frequency f2. As discussed above, the frequency f1 canbe equal to the frequency f2 or different from the frequency f2. Theantenna 11 receives the signals S1, S2 simultaneously and, thus,converts the signals S1, S2 to the composite RF signal.

[0070] Proceeding to state 804, the amplifier 14 amplifies the relativeweak composite RF signal to a level sufficient for further processing.As the amplifier 14 may cause undesired modulation products in additionto other potentially present noise components, the serially connectedfilter 16 serves to block these modulation products and noise componentsin order to minimize noise within the composite RF signal. In oneembodiment, the filter 16 is a band pass filter that limits thebandwidth of the composite signal.

[0071] Proceeding to state 806, the mixer 18 receives the amplified andband limited composite RF signal. In one scenario, for example, whilethe phone 3 is in the very proximity of the base station B1 and thus hasonly a radio connection (signal S1) with the base station B1, the phone3 operates the local oscillator 34 so that the oscillator signal LO1mixes with the signal S1 to generate the IF signal having the desiredintermediate frequency f1˜f_(LO1). The oscillator 36 can be tuned toapproximately the same frequency, i.e., f_(LO1)≈f_(LO2), so that theoscillator signal LO2 leads to the same IF signal, or the oscillator 36scans across a predetermined frequency range which allows the phone 3 todetect if another signal is present.

[0072] In another scenario, the phone 3 started to move away from thebase station B1 and closer to the base station B2. While the phone 3processes the signal S1, for example, to decode the signal S1 and todetect if another signal is present, the phone 3 tunes the localoscillator 36 to the frequency f_(LO2) so that the frequency differencef1˜f_(LO1) is in the same frequency band as described above.

[0073] Proceeding to state 808, the phone 3 has moved closer to the basestation B2 and the local oscillators 34, 36 are appropriately tuned togenerate the oscillator signals LO1, LO2. The mixer 18 is part of thefirst down conversion stage, which converts the signals S1, S2 to thelower intermediate frequency. The mixer 18 mixes the composite RFsignal, including the signals S1, S2, and the oscillator signals LO1,LO2 to generate an output signal that includes the desired IF signalwith (f1˜f_(LO1))≈(f2˜f_(LO2)) as explained above.

[0074] Proceeding to state 810, the phone 3 processes the signal outputfrom the first down conversion stage. The filter 20 separates the IFsignal from the output signal in that it passes only the IF signal. Theamplifier 22 amplifies the IF signal to compensate for losses thatoccurred through separating the IF signal from the output signal.

[0075] The processing further includes separating the IF signal in thesecond down conversion stage into the components I, Q. The IF signal issplit. One part of the IF signal is multiplied with a sine signal andthe other part of the IF signal is multiplied with a cosine signal. Thesine signal and the cosine signal are derived from the oscillator signalLO3 having the oscillator frequency f_(LO3). The second down conversionstage outputs the components I, Q which have the baseband frequencyf_(B).

[0076] Proceeding to state 812, the baseband processor 38 receives thecomponents I, Q and applies the pseudo-noise codes. The application ofthe pseudo-noise codes results in two separate signals in the baseband.These signals are further processed in the subsequent signal processingmodule 7. The signal processing module 7, for example, extracts thetraffic channel to convert the signal S2 into an analog speech signal,and analyzes the signal strength of the pilot channel. The procedureends at state 814.

[0077] In the above embodiment, the frequencies f1, f2 are allocatedwithin the same frequency band and the signals S1, S2 from the antenna11 share a common receive path up to the mixer 18. Both signals S1, S2pass through the filter 16. However, in-another embodiment of thesystems 1, 100, the frequencies f1, f2 can be in different frequencybands. In this case, the receive path of the mixer module 12 ismodified, as shown in FIG. 8, because under these circumstances one ofthe signals S1, S2 could be blocked by the filter 16.

[0078]FIG. 8 shows a section of a mixer module 12′ which is a furtherembodiment of the mixer module 12. The illustrated section includes thereceive path between the input 13 and the mixer 18′. The remainingsection of the mixer module 12′, i.e., between the mixer 18′ and theoutputs 15 a, 15 b, is as shown in FIG. 5.

[0079] The receive path between the mixer 18′ and the input 13 includesa first path having a serial arrangement of an amplifier 14′ and alow-pass filter 16′, and a second path having a serial arrangement of anamplifier 14″ and a filter 16″. The filters 16′, 16″ are connected tothe mixer 18′, and the amplifiers 14′, 14″ are connected to a duplexer40 which is further connected to the input 13 and, thus, to the antenna11.

[0080] The amplifiers 14′, 14″, like the amplifier 14 shown in FIG. 5,amplify the composite RF signal that includes the signals S1, S2. As thefilter 16 in FIG. 5, the filters 16′, 16″ can be bandpass filters or lowpass filters, each filter 16′, 16″ passing only the desired signalfrequency f1 or f2. For example, the filter 16′ is configured to passonly the signal S1, and the filter 16″ passes only the signal S2. In acellular CDMA system, the filters 16′ and 16″ are tuned to pass signalsin a frequency band between about 869 MHz and about 894 MHz. In aPCS/CDMA system, the filters 16′ and 16″ are tuned to pass signals in afrequency band between about 1930 MHz and about 1960 MHz

[0081] The mixer 18′ receives the signals S1, S2 and oscillator signalsLO1′, LO2′ generated by the local oscillators 34′, 36′. The oscillatorsignals LO1′, LO2′ have oscillator frequencies f_(LO1′), f_(LO2′),respectively. The oscillator signals LO1′, LO2′ and the signals S1, S2mix as described above. The oscillator frequencies f_(LO1′), f_(LO2′)are selected so that the output signal from the mixer 18′ has signalcomponents with f1˜f_(LO1′)≈f2˜f_(LO2′).

[0082]FIG. 9 shows an illustration of an embodiment of the mixer 18′shown in FIG. 8. The mixer 18′ includes a mixer 18 a′ connected to thefilter 16′ and receiving the oscillator signal LO1′, and a mixer 18 b′connected to the filter 16″ and receiving the oscillator signal LO2′.Each mixer 18 a′, 18 b′ is connected to a signal combiner 42 thatcombines the output signals (intermediate frequency signals) of themixers 18 a′, 18 b′ to the IF signal input to the filter 20.

[0083]FIG. 10 shows an illustration of an embodiment of the mixer 18shown in FIG. 5. The mixer 18 includes a mixer 18 a connected to thefilter 16 and receiving the oscillator signal LO1, and a mixer 18 bconnected to the filter 16 and receiving the oscillator signal LO2. Eachmixer 18 a, 18 b is connected to a signal combiner 43 that combines theoutput signals (intermediate frequency signals) of the mixers 18 a, 18 bto the IF signal input to the filter 20.

[0084] The phone 3 allows a soft handoff between neighboring cells thatoperate at different carrier frequencies. The phone 3 has two localoscillators 34, 36 and at least one of them is tunable over apredetermined frequency range to cover the frequencies used inneighboring cells or even cells of a different system.

[0085] In one embodiment, the phone 3 moves exclusively within thesystem 1 which is a cellular CDMA system. When the phone 3 moves fromone cell to another, the system 1 is configured to perform intra-systemhandoffs. In case the neighboring cells C1-C4 have the same assignedfrequency (i.e., f1≈f2), the phone 3 operates like a conventionalcellular phone. However, if the neighboring cells C1-C4 have differentassigned frequencies (i.e., f1≠f2), in accordance with the presentinvention, the phone 3 still allows performance of the “Soft Handoff.”

[0086] While the phone 3 has an active traffic connection with the basestation B1, the phone continuously monitors the signal strength of thepilot channel of this traffic connection. During the traffic connection,the local oscillator 34 is tuned so that the difference frequencyf1˜f_(LO1) is the intermediate frequency. In addition, the phone 3“listens” if it receives pilot channels from neighboring cells C2-C4.For that purpose, the phone 3 scans a predetermined frequency range bytuning the local oscillator 36 correspondingly. As soon as a(neighboring) pilot channel, for example, within the signal S2 at thefrequency f2, is present and the oscillator frequency f_(LO2) is set sothat the difference f1˜f_(LO1) falls within the same frequency band asthe difference f2˜f_(LO2), components of both signals S1, S2 fall withinthe band of the intermediate frequency defined by the filter 20. In thiscase, the phone 3 detects the presence of the neighboring pilot channel.

[0087] Once detected, the phone 3 continues to monitor the signalstrength of the neighboring pilot channel. When the signal strength ofthe neighboring pilot channel exceeds the predetermined threshold, thesystem 1 initiates the hand off from the cell C1 to the cell C2. At thetime this hand off occurs, the phone 3 is tuned to receivesimultaneously the signals S1, S2. That is, when the previous connection(signal S1) is broken, the new connection (signal S2) already exists.Although the neighboring frequencies are different, the soft handoff andits advantages are maintained. The user of the phone 3 does not noticethe hand off, because the new connection is made before the oldconnection is broken.

[0088] In another embodiment, the phone 3 moves between the systems 1,100, for example, from the cell C1 to the cell C5, and the systems 1,100 allow inter-system handoffs. Such an inter-system handoff could benecessary, for example, if the user of the phone 3 reaches a limit ofthe coverage area of the system 1 during a phone call, but continues totravel and to talk. Without an inter-system handoff, the phone callwould be terminated, eventually without a warning, because the radioconnection suddenly breaks.

[0089] The system 1 can be a conventional cellular CDMA system in whichthe neighboring cells C1-C4 operate at the same assigned frequency f1.The system 100 can be a conventional PCS system in which the neighboringcells C5, C6 operate at the same assigned frequency f3 which isdifferent from the frequency f1.

[0090] While the phone 3 has an active traffic connection with the basestation B1, the phone continuously monitors the signal strength of thepilot channel of this traffic connection. The phone 3 also monitors thesignal strengths of neighboring pilot channels of the system 1, todetermine when a handoff within the system 1 is necessary. During thetraffic connection, the local oscillator 34 is tuned so that thedifference frequency f1˜f_(LO1) is the intermediate frequency.

[0091] In addition, the phone 3 “listens” if it receives pilot channelsfrom neighboring cells C5 of the system 100. For that purpose, the phone3 scans a predetermined frequency range defined by the system 100 bytuning the local oscillator 36 correspondingly. As soon as a(neighboring) pilot channel, for example, at the frequency f3, ispresent and the oscillator frequency f_(LO3) is set so that therequirement (f1˜f_(LO1))≈(f3≠f_(LO3)) is fulfilled, components of bothsignals fall within the band of the intermediate frequency defined bythe filter 20. In this case, the phone 3 detects the presence of theneighboring pilot channel. The subsequent procedure, including the softhandoff between the cell C1 (system 1) and the cell C5 (system 100) isas described above.

[0092] While the above detailed description has shown, described andidentified several novel features of the invention as applied todifferent embodiments, it will be understood that various omissions,substitutions and changes in the form and details of the describedembodiments may be made by those skilled in the art without departingfrom the spirit of the invention. Accordingly, the scope of theinvention should not be limited to the foregoing discussion, but shouldbe defined by the appended claims.

What is claimed is:
 1. A wireless communications device forcommunications with a first base station at a first frequency and asecond base station at a second frequency, the wireless communicationsdevice comprising: an antenna configured to receive a first signal at afirst frequency and a second signal at a second frequency, said antennaconfigured to output the first and second signals as a first compositesignal; a first oscillator operable to output a first oscillator signalat a first frequency; a second oscillator operable to output a secondoscillator signal at a second frequency; and a mixer configured toreceive the first composite signal, the first oscillator signal and thesecond oscillator signal, the mixer configured to generate a secondcomposite signal with components of the first and second signalsoccupying at least a portion of a common frequency band.
 2. The deviceof claim 1 further comprising a filter connected to an output of themixer, the filter having a passband that corresponds to the commonfrequency band.
 3. The device of claim 1 wherein the first and secondoscillators are tunable within predetermined frequency ranges.
 4. Thedevice of claim 1 wherein the mixer is further configured to mix thefirst oscillator signal with the first signal so that components of thefirst signal occupy the common frequency band.
 5. The device of claim 1wherein the mixer is further configured to mix the second oscillatorsignal with the second signal so that components of the second signaloccupy the common frequency band.
 6. The device of claim 1 furthercomprising a conversion module connected to receive the second compositesignal, the conversion module configured to convert the second compositesignal to a baseband signal.
 7. The device of claim 6 wherein thebaseband signal comprises a first component and a second component. 8.The device of claim 6 further comprising a processor module incommunication with the baseband signal, the processor module configuredto process the baseband signal.
 9. The device of claim 8 wherein theprocessor module is configured to correlate the baseband signal with apredetermined function to separate the first signal and the secondsignal.
 10. The device of claim 1 wherein the first frequency is betweenabout 800 MHz and about 900 MHz and the second frequency is betweenabout 800 MHz and about 900 MHz.
 11. The device of claim 1 wherein thefirst frequency is between about 800 MHz and about 900 MHz and thesecond frequency is between about 1800 MHz and about 1900 MHz.
 12. Thedevice of claim 1 wherein the first and second signals are adapted for acode division multiple access (CDMA) system.
 13. The device of claim 1wherein the first and second signals are adapted for a personalcommunications service (PCS) system.
 14. The device of claim 1 whereinthe first signal is adapted for a code division multiple access (CDMA)system and the second signal is adapted for a personal communicationsservice (PCS) system.
 15. The device of claim 2 wherein the filter has apassband between approximately 1.25 MHz and approximately 85 MHz. 16.The device of claim 1 wherein the second composite signal comprises athird frequency which is lower than the first frequency and the secondfrequency.
 17. The device of claim 2 further comprising first and secondparallel receive paths between the mixer and the antenna, each receivepath including a serial arrangement of an amplifier and a filter andadapted to receive one of the first and second frequency signals locatedwithin different frequency bands.
 18. The device of claim 17 wherein thefilter of the first receive path blocks the second frequency signal, andthe filter of the second receive path blocks the first frequency signal.19. The device of claim 16 wherein the mixer mixes the first oscillatorsignal with the first frequency signal and the second oscillator signalwith the second frequency signal to generate a signal at the thirdfrequency.
 20. The device of claim 1 wherein the mixer is a demodulator.21. A method of receiving signals with a wireless communications deviceoperable in a communications system comprising: receiving a first signalhaving a first frequency within a first frequency band from a firstsource; receiving a second signal having a second frequency signalwithin a second frequency band from a second source; transforming thefirst and second signals into a third frequency band, the act oftransforming comprising: mixing the first signal with a first oscillatorsignal at a first oscillator frequency; and mixing the second signalwith a second oscillator signal at a second oscillator frequency,wherein the difference between the first frequency and the firstoscillator frequency, and the difference between the second frequencyand the second oscillator frequency fall within the third frequencyband; and processing said frequency-transformed first and second signalsto maintain communications with the first and second sources.
 22. Themethod of claim 21 wherein the first signal corresponds to a trafficconnection and the second signal corresponds to a signaling connection.23. The method of claim 22 wherein the act of processing includesdetermining if a signal strength of the signaling connection exceeds apredetermined threshold.
 24. The method of claim 23 further comprisingtransferring the traffic connection from the first signal to the secondsignal when the signal strength exceeds the threshold, so that aftersaid transfer the second signal corresponds to the traffic connection.25. The method of claim 21 wherein the act of transforming includesconverting the first and second signals to at least one lower frequencywithin the third frequency band.
 26. The method of claim 21 wherein theact of transforming includes converting the first and second signals atthe first and second frequencies to first and second lower frequencieswithin the third frequency band.
 27. The method of claim 26 wherein thefirst lower frequency is approximately equal to the second lowerfrequency.
 28. A method of receiving signals comprising: receiving afirst frequency signal having a first frequency and originating from afirst transmitter station and a second frequency signal having a secondfrequency and originating from a second transmitter station; convertingthe first and second frequency signals into a composite signal;generating a first oscillator signal having a first oscillatorfrequency, the first oscillator frequency being selected to have a firstfrequency difference to the first frequency; generating a secondoscillator signal having a second oscillator frequency, the secondoscillator frequency being selected to have a second frequencydifference to the second frequency; mixing the composite signal with thefirst and second oscillator signals to generate an intermediatefrequency signal, the intermediate frequency signal comprising acomponent of the first frequency signal and a component of the secondfrequency signal with the components being located within a commonfrequency band; and mixing the intermediate frequency signal with athird oscillator signal at a first phase to generate a first basebandsignal and mixing the intermediate frequency signal with the thirdoscillator signal at a second phase to generate a second basebandsignal, wherein the first baseband signal corresponds to the firstsignal and the second baseband signal corresponds to the second signal,and wherein the first phase and the second phase are approximately 90°apart.
 29. The method of claim 28 wherein the first frequency isapproximately equal to the second frequency, and wherein the firstoscillator frequency is approximately equal to the second oscillatorfrequency.
 30. The method of claim 28 wherein the first and secondfrequencies have different values, and wherein the first and secondoscillator frequencies have different values.
 31. The method of claim 30wherein the intermediate frequency signal includes the components of thefirst and second frequency signals within a common frequency band. 32.The method of claim 28 further comprising applying decoding functions tothe components of the first and second frequency signals to uncode thefrequency signals.
 33. The method of claim 28 wherein the firstfrequency difference and the second frequency difference areapproximately equal.
 34. The method of claim 28 wherein the firstfrequency difference and the second frequency difference fall within thecommon frequency band.
 35. A method of receiving signals with a wirelesscommunications device operable in a communications system comprising:receiving an input signal which comprises a first component allocatedwithin a first frequency band and a second component allocated within asecond frequency band; generating a first oscillator signal at a firstoscillator frequency; generating a second oscillator signal at a secondoscillator frequency; receiving the input signal, the first oscillatorsignal and the second oscillator signal; converting at least a portionof the first component and at least a portion of the second component toa third frequency band to produce an intermediate signal; generating athird oscillator signal comprising a sine signal and a cosine signal ata third oscillator frequency; mixing the intermediate signal with thesine signal and the cosine signal; and separating the intermediatesignal into a first baseband component and a second baseband component.36. The method of claim 35 further comprising applying pseudo-randomnoise codes to the first and second baseband components.
 37. The methodof claim 35 wherein the first oscillator frequency is different than thesecond oscillator frequency.
 38. The method of claim 35 furthercomprising generating an output signal comprising output frequencieslocated within the third frequency band.
 39. The method of claim 35further comprising isolating the third frequency band.
 40. The method ofclaim 35 wherein the third frequency band comprises a first differencecomponent corresponding to a difference between the first componentallocated within the first frequency band and the first oscillatorsignal at the first oscillator frequency.
 41. The method of claim 40wherein the third frequency band comprises a second difference componentcorresponding to a difference between the second component allocatedwithin the second frequency band and the second oscillator signal at thesecond oscillator frequency.
 42. The method of claim 41 wherein thefirst difference component is approximately equal to the seconddifference component.
 43. A wireless communications device comprising:means for receiving an input signal which comprises a first componentallocated within a first frequency band and a second component allocatedwithin a second frequency band; means for generating a first oscillatorsignal at a first oscillator frequency; means for generating a secondoscillator signal at a second oscillator frequency; means for receivingthe input signal, the first oscillator signal and the second oscillatorsignal; means for converting at least a portion of the first componentand at least a portion of the second component to a third frequencyband; means for generating a third oscillator signal at a thirdoscillator frequency; and means for converting the at least a portion ofthe first component in the third frequency band and the at least aportion of the second component in the third frequency band to abaseband frequency.